Topological interface states induced by incident angle in the 1D elastic wave system

Topological interface states are currently attracting rapidly growing attention in classical wave systems. However, little work has been done on topological interface states in one-dimensional (1D) elastic wave systems, especially in the case of oblique incidence. This paper theoretically demonstrates the realization of topological interface states of elastic waves in a 1D composite plate structure composed of two phononic crystals (PCs) with different topological characteristics, which can be regulated by the incident angle. For the out-of-plane SH mode, multiple topological interface states can coexist in different common bandgaps. For the in-plane complex P-SV coupled mode, topological interface states can exist in both "partial-polarization" and "omni-polarization" bandgaps. All these interface states are in the wide frequency and incident angle regions. We also discuss the polarization and the mode conversion of the interface states. Our results provide an innovative method to excite and tune topologically protected interface states for elastic waves, which may have potential applications in obtaining strong local vibration for different polarized elastic wave modes.